1. Field of the Invention
This invention relates to aircraft deicing apparatus. More particularly, the invention relates to a pumping system for an aircraft deicer comprising a jet pump upstream of a primary pump. The jet pump operates to increase the pressure of the fluid upstream of the primary pump above the vapor pressure of the fluid to thereby prevent cavitation in the primary pump.
2. Description of Related Art
In typical aircraft deicers, water is mixed with an aircraft deicing fluid, such as a glycol-based solution, and the mixture is subsequently applied to an aircraft requiring deicing. Industry standards require that this mixture be heated to approximately 185 degrees Fahrenheit. In a proportioning system, the water and the aircraft deicing fluid are stored separately within the deicer and are mixed upstream of the delivery nozzle. Therefore, in such a system, the water and the aircraft deicing fluid must be heated to the required temperature prior to being mixed. However, it is desirable to maintain the temperature of propylene glycol-based, or Type II, aircraft deicing fluid below 165 degrees Fahrenheit to avoid degradation of the fluid during pumping and repeated reheating of the fluid. To do this and still deliver a mixture of water and Type II fluid at 185 degrees Fahrenheit, the water must be heated to 200 degrees Fahrenheit or greater. However, in typical deicer pumping systems the water is pumped at atmospheric pressure, and when the water is heated to 200 degrees Fahrenheit, the pressure of the water at the inlet to the primary pump may fall below the vapor pressure of the water, thus resulting in cavitation.
To eliminate this cavitation problem, prior art deicers have employed larger primary pumps which are better suited to handle cavitation, secondary boost pumps upstream of the primary pumps, pressurized water tanks, and/or worm screw inducers coupled to the primary pump shaft. However, these devices are expensive and space consuming. Therefore, the most convenient solution in prior art deicers is to limit the water temperature to around 185 degrees Fahrenheit and accept a less than desirable mixture temperature.